1. Field of the Invention
The present invention relates to an improved packaging for golf balls, and more particularly, relates to a golf ball packaging that preserves the mechanical and physical characteristics of the ball during storage and transport.
2. Description of the Related Art
Golf balls generally come in two different varieties, solid golf balls and multi-piece golf balls. A solid golf ball consists of a polymeric sphere having a plurality of molded dimples which aid the flight characteristics of the golf ball. Solid golf balls are usually used for practicing, where high performance is not a priority, such as in driving ranges. Multi-piece golf balls exhibit better playing characteristics than solid golf balls and are consequently usually used on golf courses during play. A multipiece golf ball consists of either a wound or solid rubber core that is covered with a separate and distinct cover. The cover often comprises a single thermoplastic layer. Recently, new types of multi-piece golf balls have been introduced having a multilayered compound including a plastic mantle surrounding a solid polybutadiene rubber core and an external thermoplastic envelope. The solid core or the center of a wound core is generally made of an elastomer, such as a CIS content polybutadiene rubber which is combined with a zinc or other metal salt of unsaturated fatty acid. Often, small amounts of zinc oxide are also added to the core in order to achieve a higher performance in restitution, as described below.
The cover of a multi-piece golf ball is typically made from a material that contributes to the durability of the ball and also provides the particular "feel" characteristics of the ball when struck with a club. By way of example, a two-piece golf ball construction of a rubber core and an ionomer cover generally provides a very durable ball and also provides maximum travelling distance to the ball when struck with a club.
Golf ball manufacturers have recently introduced a new type of two-piece golf ball for use by the Tour players. The new golf balls provide a softer feeling to the ball when struck with a club. Manufacturers have achieved this characteristic by lowering the core compression and softening the cover of the golf ball. Golf ball manufacturers have also recently developed a three-layer golf ball having an intermediate mantle between the core and the cover. The three-layer golf ball provides a softer feel to the golf ball while also providing maximum distance and durability. In such a golf ball, it is advantageous to use a thermoplastic material for the mantle, such as a pure or blended ether block copolymer (e.g., PEBAX.RTM.), as is disclosed in U.S. Pat. No. 5,253,871.
Unfortunately, there are certain drawbacks that are associated with prolonged storage of multi-piece golf balls. Multi-piece golf balls typically absorb moisture when they are subjected to prolonged storage under ambient conditions of temperature and humidity. A short period of moisture absorption can cause significant changes in the performance characteristics of the ball. Such moisture absorption may affect the weight of the ball, as well as the physical and mechanical characteristics of the various materials that make up the different pieces of the golf ball structure, including the cover, the core and the mantle.
One other characteristic that is affected by moisture absorption is the initial velocity of the golf ball. United States Golf Association (USGA) rules govern the allowable ranges of initial velocity values for golf balls. According to the USGA rules, the initial velocity must not exceed a value of 250 feet per second, with a maximum tolerance of 2%. Consequently, golf ball manufacturers have striven to manufacture golf balls that have an initial velocity as close as possible to the 255 feet per second limit without exceeding this value.
Moisture has been shown to significantly affect the initial velocity value of a ball over a very short period of time. FIG. 1 is a graph that plots the initial velocity value as a function of time for a stored golf ball at various ambient conditions. As shown in FIG. 1, the initial velocity loss is approximately 2.5 ft/sec. over twelve months for golf balls having a soft cover, between 50 to 60 shore D, in an environment of 72.degree. F. and 50% of relative humidity (RH). Such a initial velocity loss of 2.5 ft/sec corresponds to a loss of distance of approximately 6 to 10 yards when the ball is struck with a driver. For a golf ball having a hard cover, between 68-72 shore D in the same conditions, the initial velocity loss over 12 months is approximately 0.5 ft/sec.
The problem of moisture absorption is particularly critical for soft cover balls because the soft cover is more permeable to moisture than a hard cover, so the moisture reaches the core more easily. Because it is made of a highly hygroscopic material, the core absorbs this moisture, which degrades the core's desired properties. The degradation in performance characteristics is generally accelerated when the ambient storage temperature becomes higher. For a soft cover ball at a temperature around 110.degree. F. and 50% RH, a velocity loss of 2.5 ft/sec occurs in only few weeks, as opposed to twelve months for a soft cover ball in an environment of 72.degree. F. and 50% RH. During transportation of the golf balls from the manufacturing facility to a retail store, actual storage conditions are closer to these conditions. Consequently, soft cover balls may experience a large reduction in performance characteristics when being transported from the manufacturing facilities to the retail store.
Three-layered golf balls also encounter a similar problem with moisture absorption. A three-piece golf ball including a polyamide-base mantle, such as PEBAX.RTM., is sensitive to water absorption. The characteristics of such a golf ball can change significantly during a short period of time if the ball absorbs moisture. In particular, the characteristics of hardness, weight, volume, tensile strength, elongation, resiliency, and modulus can vary significantly after a prolonged stay in ambient conditions and be worse in humid and warm conditions.
Golf ball manufacturers have proposed various golf ball structural configurations in an effort to inhibit moisture absorption. United Kingdom Patent Application 2,280,379 proposes to include in the golf ball structure a moisture barrier layer that has a lower water vapor transmission rate than the golf ball cover. The golf ball includes a cover that has a thickness of at least 30 mils and a continuous moisture barrier layer that surrounds the inner core. While this golf ball is designed to increase the shelf life of a ball by inhibiting moisture absorption, it also presents many drawbacks. First, the moisture barrier layer is generally made of a material that does not readily adhere to the adjacent materials in the golf ball structure. Consequently, the various layers of the golf ball structure may move relative to one another, such as through rotation. As a result of this lack of adhesion between the layers, the spin rate of the ball is reduced since the momentum transferred to the ball is significantly less than if the inner layers initially moved at the same rate as the outer layers. Second, the acceptable thickness of the moisture barrier layer is limited, as the characteristics of the ball would be adversely affected if the barrier layer constituted a major portion of the ball structure. Consequently, the moisture barrier layer must be made relatively thin. However, if it is made too thin, the moisture barrier layer will not sufficiently inhibit moisture absorption, so that the moisture barrier layer must generally be used in conjunction with a cover that is relatively thick, which may be undesirable.
United Kingdom Patent Application 2,280,379 also discloses a golf ball having a moisture barrier layer positioned outside the golf ball clear coat. The clear coat is a solution that is applied to the outer surface of a golf ball to protect the ball and to add an aesthetically pleasing appearance by providing the ball with a high gloss and mirror-like finish. Unfortunately, positioning the moisture barrier layer outside the clear coat is undesirable since it may subject the moisture barrier layer to damage during use. Another drawback associated with placing a water barrier around the clear coat is that the barrier layer significantly reduces the clear coat's transparency and glossy appearance. This may adversely affect the appearance of identifying indicia, such as trademarks, logos, model names, etc., that are often placed on the golf ball. Finally, the golf ball of U.K. Application 2,280,379 is complicated to manufacture and involves steps for which special precautionary measures are required. For example, the core is dipped in a solvent solution, such as toluene, which is a known toxic and cancer-causing chemical.
Japanese Patent Application No. 7-187268 discloses a packaging for golf balls. The packaging is made of a heat-shrinkable film that is shrunk over golf balls for storage. The film enables the golf balls to be arranged in a tight configuration of lines or rows. Perforations are made in the film to facilitate the evacuation of air during the process of heat-shrinking the film. While this type of packaging eliminates bulk by enabling a collection of golf balls to be tightly packed, it does not address the problem of moisture absorption by the golf balls after they are packed and during storage. The packaging disclosed in JPA 7-187268 does not act as a moisture barrier, as the perforations in the packaging make it permeable to moisture.
Currently, manufacturers pack golf balls that are available on the market in rigid paper or cardboard boxes. Such packaging is highly susceptible to moisture penetration and, therefore, moisture absorption by the golf balls. As discussed above, such moisture absorption greatly reduces the performance characteristics of the ball.
There is therefore a need for a packaging that may be used to store golf balls prior to first use and prevent the damage associated with difficult storage and shipping conditions, such as temperature and moisture. Such a packaging should sufficiently protect the golf ball to ensure the freshness of the golf ball and preserve the optimum properties of the golf ball prior to first use, while also preserving and protecting the structure of the ball. The packaging should be both capable of protecting single or multiple golf balls and retaining the physical and mechanical properties of the ball, such as the initial velocity value, until the packaging is opened.